Sunday marks 100 days until the November midterm elections. / Markell DeLoatch, AP

by Susan Page, USA TODAY

by Susan Page, USA TODAY

WASHINGTON - In 100 days or so, Democrats and Republicans will know whether the bets they're placing for the November midterm elections pay off - or don't.

Republicans are hammering President Obama, the officeholder not on any ballot who GOP strategists argue defines the election anyway. Obama is trying to persuade skeptical Americans that the economy is brightening. Democrats are targeting women voters, especially unmarried women, who tend to be supporters but may not bother to go to the polls this year.

At stake is control of the Senate, where the Democratic majority is imperiled, and the political landscape Obama will have to negotiate during the final two years of his White House tenure. The lessons learned from now until Election Day (precisely 100 days from Sunday) will be scrutinized for the presidential and other contests to follow in 2016.

"The question is how horrible is Obama's brand and what effect is that brand going to have?" Republican National Chairman Reince Priebus said when asked in an interview what to watch for over the next three months. Not surprisingly, his Democratic counterpart, Florida Rep. Debbie Wasserman Schultz, disagrees. "Republicans are desperate to distract ... from an agenda that is truly extreme because they have been engulfed by the Tea Party," the Democratic National Committee chairwoman said.

Democrats face headwinds from history and happenstance. Since World War II, six presidents have been elected to the White House twice. In the sixth-year midterms for the previous five, the president's party has lost an average of six Senate seats and 27 House seats. What's more, six of the Senate races this year are Democratic-held seats in unfriendly territory - states that Republican Mitt Romney carried two years ago.

Republicans need a net gain of six seats to win control of the Senate.

It will be the first big Election Day since the central provisions of the Affordable Care Act went into effect - with difficulty, given the botched rollout of HealthCare.gov last fall - and Supreme Court decisions that opened the door to vastly more campaign spending continue to reverberate.

In recent days, cascading crises abroad - including the Israeli invasion of Gaza, the rising insurgency in Iraq and the shootdown of a Malaysian commercial airliner over Ukraine - have spotlighted foreign policy as a potential wild card. "Domestic issues certainly far outweigh foreign issues at this moment, but the world is in such a precarious place at the moment, it's possible that would change," Democratic pollster Mark Mellman says.

There are 36 Senate and 36 gubernatorial races this fall, plus contests in all 435 House districts. What will we know when the votes are counted Nov. 4? Which campaign arguments and strategies worked?

Here's a look at three key ones.

1. YOU'RE BETTER OFF THAN YOU WERE - REALLY

Americans are unhappy about the way things are going in the USA. In the Gallup Poll, three-quarters express dissatisfaction with the country's direction. One in four Americans, including only about a third of Democrats, are satisfied.

Obama is trying to make the case that the economy significantly has improved and that he deserves some of the credit. "By almost any measure, we are better off now than where we were when I took office," the president told a friendly audience in Austin this month. "Some of it had to do with decisions we made to build our economy on a new foundation."

The evidence: 10 million jobs created since the nadir in early 2010 and an unemployment rate that dropped to 6.1% last month. The value of 401(k) retirement accounts at record highs last month, according to a Fidelity Investments analysis released Monday. A surge in the stock market. An energy boom.

In a speech in Washington pegged to Independence Day, Obama said he hoped "the American people look at today's news and understand that, in fact, we are making strides."

"Democrats may do better than people think if you look at the economy and consumer confidence," says Sara Fagen, a Republican strategist and former White House political director for George W. Bush. But she cautions, "There's a bifurcated economy right now where some people don't feel so good."

That fact complicates the president's argument. Many Americans, especially the long-term unemployed, continue to struggle. Though home prices have rebounded, they remain below pre-recession levels. Most importantly, median household income, adjusted for inflation, is about 5% lower than it was when Obama was inaugurated in 2009.

"His problem is what they're going to hear is an excuse," says Republican pollster David Winston, an adviser to House Speaker John Boehner. In Winston's surveys, Americans agree the economy has gotten better since the financial meltdown in 2008 but say it's not good enough. "They want to hear, OK, what are you going to do?"

Mike Shields, chief of staff for the Republican National Committee, says economic concerns remain one of the "pillars" that make him confident of a strong election for the GOP in November. The others include an enthusiasm gap that favors Republicans, a "weak Democratic brand" - and the Affordable Care Act.

2. DOES OBAMACARE PACK A POLITICAL PUNCH?

Shields doesn't call the health care law the Affordable Care Act, of course. He calls it Obamacare, the most controversial legislation of Obama's presidency and one that has turned out to be a political asset for the GOP since it was signed four years ago.

That year, the furor over the law was a major issue in elections that gave Republicans control of the House. Since then, unyielding opposition to the Affordable Care Act has energized the Republican base and stoked suspicion about the law and its impact. A federal appeals court in D.C. ruled Tuesday that the consumer subsidies at the heart of the law couldn't be offered in states that use the federal exchange, a potentially devastating blow, although an appeals court in Richmond upheld the subsidies a few hours later.

"The way the Republicans and their outside allies use the Affordable Care Act has done real and lasting damage; I think there's no debating that," Mellman says. But he and other Democrats say its political potency finally may be fading. "I think people are getting tired of it, however. We see a lot of evidence of that. In focus groups, people say when an Obamacare ad comes on TV, 'I turn them off.' "

New York Rep. Steve Israel, chairman of the Democratic Congressional Campaign Committee, notes House Republicans have stopped scheduling largely symbolic votes to repeal the law. "It's backfiring," he says of the repeated repeal votes and a renewed investigation into the Benghazi attacks in 2012 that killed four Americans in Libya. "The message to their base is alienating and losing moderate, persuadable voters, and it's also firing up our base."

Maybe so, but GOP candidates continue to put their money in attacking Obama and his eponymous legislation.

For the first six months of the year, Obamacare was the most frequently mentioned issue in Republican advertising, according to tracking by Elizabeth Wilner at Kantar Media Intelligence/CMAG. She identified 94 individual ads blasting Obama and 78 targeting health care in competitive House, Senate and gubernatorial races.

In contrast, Democratic candidates rarely mention the president in their ads.

"As someone who has watched every political ad so far this cycle, in a nutshell, on the Republican side, almost everyone" mentions Obama, Wilner says. "On the Democratic side, hardly anyone."

In past midterms, a president's job approval has been one of the most reliable indicators of how candidates in his party will fare. At an anemic 42% in the Gallup Poll, Obama's rating stands 6 percentage points better than George W. Bush at this point in his second term, a year in which Bush acknowledged his party took "a thumping." Obama lags Dwight Eisenhower, Ronald Reagan and Bill Clinton by double digits.

"There's an old saying, 'The fish rots at the head,' " Priebus says. "Barack Obama is the CEO; he's the president of our country; and if things are going well or people perceive things aren't going well, they're going to place the blame at the foot of the CEO."

3. WOOING WOMEN, ESPECIALLY SINGLE ONES

Less than two years ago, Obama won a second term, the only Democrat since World War II to carry two presidential elections with a majority of the vote. Why does he seem more of a problem than an asset for Democrats now?

One big reason is the difference in who is likely to show up to vote.

"I've been through election cycles where our base is not motivated, and it's not fun," Shields says, mentioning 2006 and 2012. This time, "it looks a lot like 2010 in terms of how independents break and how motivated our base is going into the midterms."

That was a year in which Democrats lost six Senate seats and control of the House. A poll by Democracy Corps and Women's Voices Women Vote Action Fund concluded that turnout among key Democratic voter groups important for Obama's victory in 2012 - unmarried women, minorities and those under 30 - "are underperforming even 2010 margins, which was a terrible year."

That means the midterm electorate is poised to be older, whiter and more male. In a word, more Republican.

Unmarried women make up more than one in four eligible voters, but the report by Democratic pollster Stan Greenberg and others concluded that, as things stand, almost one-third of the unmarried women who voted in 2012 won't turn out in 2014. After African Americans, they are among those who most reliably support Democrats.

Whether women can be persuaded to go to the polls will decide what happens in November, Wasserman Schultz says: "Their participation in their election will, I think, be determinative in the outcome."

"It's all about economics for the women who are going to decide this election," says Stephanie Schriock, president of the Democratic PAC Emily's List.

Congressional Democrats are pressing a series of measures unlikely to pass by November but tailored to appeal to the concerns of many unmarried women: raising the minimum wage, ensuring equal pay, responding to a Supreme Court decision that allows some employers to refuse to provide insurance coverage for birth control. They accuse Republicans of waging "a war on women."

Shields calls that "a false narrative" Republicans are countering.

Priebus scoffs at the Democratic focus on women. "They're a one-trick pony, and they don't have a lot of options," he says, calling the Affordable Care Act "a roadblock" for Democrats in making their case to women voters.

Both sides say there's time to shape the election over the next 100 days.

"Politics is a song, and people don't really listen to the lyrics for a while â?? until September, October, when they have to make a decision," Democratic consultant Jamal Simmons says. "I don't think everything is set."